The purpose of the Electoral College is to aggregate votes at the regional level (some are winner-take-all, some aren't). Different states have different values. California is very different from Wyoming. And Florida is very different from Kentucky.

The problem with a straight popular vote is that you end up with results that are only aggregated by class or ideology. In 2016 this would have been essentially the big cities winning and rural America losing. We're approaching a tipping point where in every election the popular vote will go to the liberal candidate.

That may seem like a good idea on the surface if that means your candidate wins. However, in the long run it would cause massive division in the country because rural America and its values wouldn't be represented at all. Politicians would only campaign in big population centers. The end result of that is essentially portrayed in the Hunger Games, where you have the Capitol with all the power and a rural underclass doing all the work and production until they revolt. That isn't good for America or Americans.